Shoulder prosthesis

ABSTRACT

A shoulder prosthesis having a head and an elongate stem portion including a proximal end connected to the head, a distal section for insertion into a medullary canal of a humeral bone and an alignment section disposed between the proximal end and distal section. The alignment section includes a plurality of reference marks positioned to facilitate placement of the prosthesis in the bone at a previously determined position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/191,928, filed Nov. 13, 1998, which is a continuation-in-part of U.S.patent application Ser. No. 09/040,504, filed Mar. 17, 1998, issued asU.S. Pat. No. 5,961,555 on Oct. 5, 1999, which is a CIP of Ser. No.09/165,475, filed Oct. 2, 1998.

This invention relates generally to bone prostheses and moreparticularly to a shoulder prosthesis.

BACKGROUND OF THE INVENTION

When a joint, such as the hip or shoulder, becomes impaired due toarthritis, disease or trauma, it is sometimes necessary to replace allor part of the joint with a prosthesis to restore function. Forinstance, hip replacement, where a prosthesis is provided to replace thefemoral head and in some cases all or part of the acetabulum, has becomea common procedure to treat femoral head fractures and arthritis inelderly patients. As a result of anatomical constraints and challengesin the shoulder, shoulder implants have historically been much lesssuccessful and less common than hip replacements. Recently, however,shoulder arthroplasty has emerged as an accepted treatment for severearthritis and humeral head fractures.

As a consequence of the increasing acceptance of shoulder prostheses,many different devices have been developed to address various problemsthat have arisen and to offer additional benefits and features. In thesimplest form, a shoulder prosthesis is formed as a single piece with ahead to articulate with the glenoid cavity, and a stem to extend downthe medullary canal of the humerus and support the head. While simple toconstruct, unitary implants do not offer any adjustability toaccommodate the natural variations in size and geometry that occur amongjoints of different patients. To accommodate these variations, a largestock of devices must be manufactured and maintained to insure that anadequate match can be achieved during an operation. Stocking the largenumber of devices is a significant expense with one-piece designs, andin some cases a surgeon may not be provided with sufficient flexibilityto achieve an ideal fit to the patient.

To avoid the expense of maintaining a large stock of single-pieceprosthetics and to provide increased flexibility to surgeons, manyshoulder implant makers have gone to a modular design that is assembledduring the operation from two or three pieces. These pieces include ahead to articulate with the glenoid and a stem structure on which thehead is mounted and secured to the bone. In some cases, the stemincludes a separate body portion disposed between the head and anintermedullary portion of the stem that extends down the medullarycanal. By utilizing a modular design, a wide variety of devices can beassembled from only a few pieces, thus providing increased flexibilityto accommodate anatomical variation and eliminating much of the costassociated with maintaining a large selection of one-piece devices.

Existing modular shoulder designs most commonly rely on a taper lockmechanism to secure the head to the rest of the implant. In at leastsome devices the portion of the taper lock on the head is offset tocompensate for anatomical posterior offset of the humeral head. Forinstance, the taper lock portion on the head may be offset by 2-4millimeters. By rotating the head, any offset between plus and minus the2-4 millimeters can be achieved. Unfortunately, rotating an offset headcan introduce a medial/lateral and/or superior/inferior offset at thesame time the anterior/posterior positioning is adjusted. Furthermore,the offset between the center of the taper lock and the geometricalcenter of the head creates a torque which tends to rotate the headrelative to the remainder of the implant, thereby increasing the chanceof loosening of the head. As the offset increases, the resultant torqueincreases as well, making this a greater problem for larger offsets.Although such problems are incumbent in existing offset head designs, aposterior offset is generally desirable to better match the naturalanatomy.

In addition to the specific drawbacks associated with various existingimplant designs, there are a number of general problems inherent inshoulder replacements. In particular, it is generally difficult toestablish the proper position and orientation for the implant in thehumerus. One of the more important variables is the rotational position,or retroversion, of the head on the humerus. Anatomically, the averageretroversion between a plane defined by the perimeter of the anatomicalhead and the axis of the flexed forearm is approximately 30-degrees.Unfortunately, with existing implants and techniques for theirinstallation, it has been very difficult to reliably reproduce desiredretroversion. Establishing correct retroversion is important becauseincorrect retroversion can lead to problems with subsequent dislocation.

In addition to the retroversion of the implant, it is necessary toestablish the correct height of the implant on the humeral shaft. Withexisting designs, the surgeon slips the stem into the medullary canaland makes an educated guess at the proper height. Excess height maycreate too much tension in the deltoid, while inserting the implant toofar down the humerus can result in deltoid lag. Similarly, the offset ofthe face of the head relative to the stem must be established correctlyor excess or insufficient tension in the rotator cuff may be created.Unfortunately, with existing designs there is no way to evaluate implantheight or head offset prior to final installation, after whichcorrection is difficult.

SUMMARY OF THE INVENTION

The present invention is a shoulder prosthesis having a head and anelongate stem portion including a proximal end connected to the head, adistal section for insertion into a medullary canal of a humeral boneand an alignment section disposed between the proximal end and distalsection. The alignment section includes a plurality of reference markspositioned to facilitate placement of the prosthesis in the bone at apreviously determined position.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded isometric view of a modular shoulder implantconstructed according to the present invention.

FIG. 2 shows a modular shoulder implant kit constructed according to thepresent invention.

FIG. 3 is a cross-sectional view of a shaft of the implant of FIG. 1.

FIGS. 4-9 are various views of a body portion of the implant of FIG. 1.

FIGS. 10-13 are various views of a head portion of the implant of FIG.1.

FIG. 14 is an isometric view of the backside of the head of FIGS. 10-13.

FIG. 15 is an isometric view of the head partially installed on thebody.

FIG. 16 is a cross-sectional view of the implant along line 8—8 of FIG.3.

FIG. 17 is a medial elevational view of the implant of FIG. 1.

FIG. 18 is an isometric view of a targeting/installation instrumentaccording to the present invention.

FIG. 19 is a lateral elevational view of the targeting/installationinstrument of FIG. 10.

FIG. 20 is an elevational view from above of the targeting installationinstrument of FIG. 18.

FIG. 21 is an isometric view of the implant of FIG. 1 in an assembledconfiguration.

FIG. 22 is a side elevational view of an implant showing referencemarks.

FIG. 23 is a side elevational view of a body constructed according tothe present invention.

FIG. 24 is an elevational view of the rear surface of a head constructedaccording to the present invention.

FIG. 25 is an elevational view along line 25—25 in FIG. 23.

DETAILED DESCRIPTION

A shoulder implant constructed according to the present invention isshown generally at 10 in FIG. 1. Implant 10 includes a head 12 and astem 14. The stem preferably includes a distal shaft 16 and a body 18.The components making up implant 10 are preferably chosen from a kit 20of interchangeable shafts, bodies and heads, as shown in FIG. 2. Byselecting an appropriate shaft, body and head from kit 20, a surgeon isable to create an implant that is sized properly for almost any patient.It should be noted that positional references such asanterior/posterior, medial/lateral and proximal/distal used herein aremade with reference to an implant as it would be positioned in apatient.

Shaft 16 is shown in greater detail in FIG. 3 and includes a proximaltapered end 30 extending distally to a shoulder 32 which tapers smoothlyinto a cylindrical medial region 34 with distal locking holes 36, 38. Ascan be seen in FIG. 2, the shaft can have a medial region of varyingdiameter and/or varying length. Generally speaking, the longer shaftsare used where there is a mid-shaft fracture in addition to the proximaltrauma. The varying diameter short shafts are used to accommodate sizevariations in the proximal end of the humerus. Either or both of holes36, 38 may be elongated to allow for movement of the medial region overthe locking screws. This is normally desirable when the implant is usedto treat a combined mid-shaft fracture.

A rounded and tapered distal tip 40 is formed on the end of medialregion 34. Shaft 16 preferably includes a central canulation 42 whichcan be used to guide the implant into the humerus with the aid of aguide wire. As best shown in FIG. 1, an alignment notch 44 is formed inshoulder 32 to aid in establishing the correct orientation of the bodyon the shaft, as will be described below. A threaded hole 46 is formedin tapered end 30 to receive a screw 50 which is used to draw the bodyfirmly onto the tapered end. A wiring hole 48 is provided just distal ofshoulder 32 to allow tension band wiring to be secured through theimplant. In addition, when the implant is to be cemented in place, aK-wire can be driven through humerus and hole 48 to fix the position ofthe implant while the cement cures.

As indicated in FIG. 1, body 18 mounts to the top of shaft 16. Referringto FIGS. 4-9, body 18 has a distal end 54 with a cylindrical taperingsocket 56 extending upwardly therefrom into the body. Socket 56 is sizedto receive tapered end 30 of shaft 16 and taper-lock thereto to allowthe body to be securely mounted to the shaft. A proximal bore 58 extendsfrom the socket to the top of the body to the previously discussed screwto engage the top of the shaft to draw it into the socket. A small rib60 is provided in the bore to engage against the head of the screw.

A small finger 62 projects down from the distal end of body 18 adjacentthe socket to engage alignment notch 44 as the body is installed on theshaft. See FIGS. 1 and 17. This ensures the proper rotationalpositioning of the body on the shaft so that the various holes in theshaft are oriented correctly. Body 18 further includes a lateral rib 64with three suture holes 66 which aid in securing the fracture fragmentsto the implant. Upper and lower medial suture holes 68, 70 are alsoprovided in body 18 to offer additional options in securing thefragments. A medially-positioned, anteriorly-oriented threaded hole 72is formed in body 18 to receive a screw for securing the head to thebody. Hole 72 also serves as a mounting point for atargeting/installation instrument used with the implant. A recess 74 islocated at the top of the hole and includes a keying notch 76 fororienting the targeting/installation instrument. See FIGS. 1 and 4. Therecess allows the screw head to install substantially flush with thesurface of the body to minimize the amount of bone removal required toinsert the stem into the humerus.

Body 18 includes a medially-facing inclined mounting surface 80 at theproximal end onto which head 12 is mounted. Head 12 is secured to body18 by coupling structure 82 which includes a fitting in the form of apedestal or dovetail 84 located on mounting surface 80. As shown inFIGS. 6 and 8, dovetail 84 is tapered from anterior to posterior toestablish a taperlock with the head, as will be described below. Becausethe dovetail is tapered, the body has a left or right orientationdepending on which shoulder is to be replaced. Thus, as shown in FIG. 2,the kit will preferably include two or more bodies. Additional bodies,over and above one left and one right, may be provided to accommodatedifferent stem diameters or head angles, etc.

Head 12, which is preferably formed as a unitary member, as opposed tobeing assembled from two or more components, includes a generallysemi-spherical articulation surface 90 which is adapted to engage theglenoid cavity in the shoulder. See FIGS. 10-13. Because the glenoidcavity does not define a close fitting socket, such as found in theacetabulum in the hip joint, the articulation surface only needs to besufficiently spherical to allow smooth articulation in the glenoidcavity.

As best shown in FIG. 14, articulation surface 90 is bounded by anarticular margin 92 which defines an articular plane 94 generally normalto a head axis 96. In the preferred embodiment, where the head issubstantially spherical, the head axis represents a central axis ofrotational symmetry for the articulation surface and a center ofcurvature 98 lies on the head axis. See FIG. 11. As shown by the dottedlines in FIG. 13, the various heads are preferably formed with the sameradius, but simply represent larger portions of a sphere. It is believedthat this best reflects the actual anatomical characteristics.

In the most commonly occurring fracture pattern, the anatomic headfractures generally through the articular margin and plane. Thearticular plane defines generally the distal extent of head 12. This isimportant when it is necessary to remove the head as part of a revisionprocedure, because the present invention allows the head to be removedfrom an anterior direction without dislocation of the joint and theassociated trauma. This is not the case with existing implant heads,which cannot be separated from the body for removal without firstdislocating the joint. It is desirable, although not required, that thehead not project substantially beyond the articular plane in the presentinvention so that it is possible to slide the head out of the joint inan anterior direction without disruption of the surrounding bone.Because the remainder of the humerus is distal to the articulationplane, the head may be slid out in that plane without disruption of thesurrounding bone as long as the head does not project substantiallybeyond the articular plane. Thus, the coupling structure is adapted toallow the head to be installed on and removed from the stem withoutdislocating the shoulder after the implant has been installed in theshoulder.

Head 12 includes a mounting surface or backside 100 disposed oppositethe articulation surface and separated from the articulation surface bythe articular margin. Backside 100 includes a portion of couplingstructure 82 in the form of a transverse track or undercut channel 102.Channel 102 is cut to match the cross-sectional shape and taper ofdovetail 84 and includes an open end 104 and an inner end 106. Acylindrical recess 108 extends from the perimeter of the head past theinner end of the channel and to a stop 110. A groove 112 is formed inrecess 108 near the edge of the head.

The channel is sized so that the head is guided onto the body and thedovetail taperlocks in the channel when the head is properly positioned.See FIG. 10. The taperlock connection is important because it rigidlysecures the components and prevents them from fretting against eachother and generating debris over time. The coupling structure of thepresent invention may also be described as a transversely acting taperlock, with a portion of the taper lock being disposed on the head and aportion disposed on the body. The taper lock of the present invention istransverse acting in that it does not rely on motion along the axis ofthe head to lock, contrary to existing designs. In fact, it can be seenthat, when the head is engaged on the stem, the coupling structuremechanically interlocks the head against motion transverse to thearticular plane. This is in contrast to existing designs, which simplyrely on a frictional interconnection in the direction transverse to thearticular plane.

A locking member in the form of a screw 114 is provided to draw the headfirmly onto the body to properly seat the taperlock. In particular,after head 12 is initially positioned on the body, as shown in FIG. 15,it is slid generally into position and screw 114 is installed into hole72 with the head of the screw fitting closely into cylindrical recess108. See FIG. 16. As the screw is driven in, the head of the screwengages stop 110 to pull head 12 firmly onto body 18. Screw 114 alsoserves as a backup interlock to insure that the head does not becomedislodged. It should be noted that the head of the screw will not seatcompletely against the body because some space must be left toaccommodate machining tolerances in the coupling structure so that thetaper lock may be drawn tight in all cases.

When it is necessary to remove the head, as in a revision, a tool 120with a flange 122 secured near the tip of the tool is utilized. See FIG.16. The tip of the tool is initially installed in the screw head from aslight angle away from the head and then the tool is rotated toward thehead to engage the flange with taper breaking surface in the form of agroove 112 formed in recess 108. As the screw is backed out, the flangepulls against the head to dislodge the taperlock. Thus, the head can beremoved with application of external force to the implant, as has beenrequired with prior designs. This reduces the chance that the entireimplant will be loosened when only the head needs to be removed.

Installation of the implant of the present invention is facilitated by atargeting/installation instrument, shown generally at 130 in FIG. 18.Instrument 130 includes a template member 132 to which are mounted amounting bar 134, a height adjusting mechanism 136 and a retroversionguide 138. Mounting bar 134 serves to join template member 132 toimplant 10. In particular, bar 134 is hollow and includes a tab 140 (notshown) at the free end. The bar receives a bolt 142 with a head 144 anda threaded end 146. To attach the instrument to the implant, the freeend of the bar is placed in recess 74 and aligned so that tab 140 fitsinto keying notch 76. This establishes the correct alignment between thetemplate and the implant. The threaded end of the bolt is then screwedinto hole 72 to secure the instrument to the implant. The bar includes aflat 148 to allow the bar to reach body 18 without engaging head 12. Inaddition, it should be noted that the screw which secures the head tothe body is not installed until after the instrument is removed.

Once the instrument is mounted to the implant, the stem is inserted intothe shaft of the humerus. In the typical fracture pattern, the head andgreater and lesser tubercles are separated from the remainder of thehumerus, leaving a pipe-like upper shaft. As a result, there is noremaining reference for the correct height of the implant head relativeto the top of the humeral shaft. It is important to position the head atthe correct height relative to the humeral shaft to avoid excess tensionon the deltoid muscle by having the head too high or deltoid lag wherethe head is too low and the deltoid must undergo some contraction priorto starting to move the arm.

The height adjusting mechanism allows the surgeon to temporarily set theheight of the head and then evaluate the deltoid tension. In particular,as shown in FIGS. 18 and 19, height adjusting mechanism 136 includes aguide bar 150 which is moveably mounted to a carriage 152, which isdriven up and down along a threaded rod 154. With the implant in ahumeral shaft 156, the guide bar is positioned to sit on top 158 of thehumeral shaft. The surgeon can then adjust the implant up or down byturning the threaded rod. The guide bar establishes a predeterminedheight, which can be maintained while retroversion is set and even ifthe implant is removed and reinserted, as when bone cement is used.

After establishing the correct height the surgeon can use theretroversion guide to set correct retroversion, as shown in FIG. 20. Theretroversion guide includes an L-shaped rod 160 with a lower sightingarm 162. Rod 160 is pivotally and slidably mounted to template 132 toallow the height and angular orientation of the sighting arm to beadjusted. A set screw 164 allows the position of the rod to be fixedonce it is in the desired orientation. In use, the sighting arm is setfor a predetermined retroversion angle relative to the head axis, forinstance 30-degrees. This can be accomplished before attachment to theimplant using a protractor jig (not shown). With the sighting arm set tothe correct orientation, the patient's forearm is flexed toapproximately 90-degrees to the humerus. The surgeon then rotates theimplant to align the sight arm with the axis of the forearm, therebyeasily and accurately establishing the desired retroversion.

Once the correct height and retroversion is established, a cannulateddrill guide 170 is inserted through guide holes 172 provided in thedistal end of the template member. See FIG. 18. Guide holes 172 areoriented to target locking holes 36 in the end of the stem. A drill 174is inserted though the drill guide to bore through the bone over thelocking holes. One or two screws are installed through the humerus andlocking holes to secure the implant in place.

As shown by the dotted lines in FIG. 19, it is possible to attach thegreater tubercle 159 to the implant prior to final securing of the head.This allows the surgeon to evaluate the tension in the rotator cuff andmake corrections, if necessary, by moving to a smaller or larger head.One other feature of the present invention is the provision of suturesupports 180, shown in FIG. 21, which serve to distribute the force ofthe suture over the bone. Particularly in trauma cases, the bone is verysoft and without supports 180, the sutures will sometimes pull throughthe bone. By utilizing the supports, the surgeon can obtain the desiredsuture tension without risk of the suture pulling through the surface ofthe bone.

It should be noted that the targeting/installation instrument isprovided in left and right versions, although it would also be possibleto make mounting bar 134 reversible or symmetric to accommodate left andright bodies. In addition, a longer template member would be used withthe longer shafts used to treat mid-shaft fractures.

Installation and alignment of the implant can also be facilitated byplacing indications or reference marks on the implant as shown at 200 inFIG. 22. Reference marks 200 are placed in an alignment section 202 ofthe stem, generally in the area of the stem which will lie adjacent thetop of the humeral shaft when installed. Preferably, the reference marksinclude one or more angular marks such as angular indication 204 andmultiple vertically-spaced gradations 206, allowing both height andangular orientation to be monitored. A plurality of indicia such asletters 208 are applied to the vertically-spaced gradations marks atintervals to make identifying a particular gradation easier. The markscan be laser marked on the surface of the implant, etched into theimplant or applied via any other standard marking process. It should benoted that the marks and indicia would normally be viewed from theanterior direction and are therefore preferably placed on that side. Inthe case of implants that can be placed on either the left or rightside, the marks and indicia would preferably be formed on both sides ofthe implant so that they were visible in either case.

In use, the surgeon first installs one or more trial prostheses toobtain proper fit and positioning in the fashion described above. Thetrial prostheses are typically identical to the actual prosthesis, butare assembled from a kit of components that are reused from operation tooperation. The trial prostheses are equipped with reference marks at thesame locations as the actual prosthesis. Once the correct fit andpositioning are established, the surgeon notes which gradation ispositioned adjacent to the top of the humeral shaft. The surgeon thenmarks the bone with a methylene blue dye marker at the top of the shaftin line with the angular indication. The surgeon can then take theactual implant and place it in the bone and replicate the trialposition, which includes an angular orientation and a depth component,by aligning the previously-noted marks on the actual implant with thepreviously-determined location on the bone.

It should be understood that the alignment marks could be implemented ona modular or unitary implant and could be used alone or in conjunctionwith the above-described targeting instrument. Moreover, such marks arebeneficial, even when used without a trial device, to verify that animplant has not moved after the desired position has been established.

Another embodiment of a body for use with a shoulder implant accordingto the present invention is shown at 218 in FIG. 23. Body 218 is similarin construction to body 18, but includes a tapered stud 222 formed on anupper mounting surface 280. A head 212 is adapted to be mounted to body218 by mounting on stud 222. More specifically, the head includes atapered bore 226 which fits over stud 222 and is sized to form a taperlock therewith, thus securing the head to the body. A collar 224 formsthe lower boundary of mounting surface 280. See FIG. 24. The collarserves to prevent the body from subsiding down into the humerus andcreating an outward pressure on the head tending to loosen the taperlock.

As best seen in FIG. 25, the axis of the tapered stud is offset from ananterior/posterior plane 228 of the body and stem. In the disclosedembodiment, the offset, indicated at 229, is approximately twomillimeters in the posterior direction, as implanted. Generally,suitable offset could be between approximately 1 and 5 millimeters. As aresult of the offset, the bodies are provided in left and right versionswhich are mirror images of each other.

In the disclosed embodiment, the tapered bore is positionedapproximately 1 millimeter offset from the center of the head asdepicted at 227 in FIG. 24. This offset allows the surgeon to rotate thehead to achieve any desired offset between 1 and 3 millimeters. Byoffsetting the tapered stud from the anterior/posterior plane, thesurgeon is able to achieve a range of posterior offsets withoutintroducing excessive superior/inferior offsets. Although the head isshown with an offset, it is possible that the head might not have anyoffset, thus eliminating any superior/inferior offset. One of thebenefits of eliminating head offset is that it is possible to introducethe desired anterior/posterior offset via the body without introducingother perturbations into the positioning of the head. It is generallydesirable to keep the head offset to a minimum to reduce the torquecreated by the offset.

In addition to providing the body in left and right versions, it may bedesirable to provide multiple left and right bodies with variousoffsets. Because heads are substantially more costly to produce thanbodies, providing multiple bodies offers a more economical approach toachieving a wide variety of anatomical offsets. The body can bemanufactured by machining from bar stock or may be cast. Another benefitof providing side-specific bodies is that the size of the body can bekept to a minimum in comparison to adjustable bodies. Minimizing thesize of the body reduces the amount of bone that must be removed toinstall the implant.

It should be noted that the anterior/posterior offset described in thecontext of a cylindrical taper lock could also be implemented on thedovetail taper lock previously described by simply offsetting the taperlock in the head or on the body or both.

While the invention has been disclosed in its preferred form, thespecific embodiments thereof as disclosed and illustrated herein are notto be considered in a limiting sense as numerous variations arepossible. Applicant regards the subject matter of his invention toinclude all novel and non-obvious combinations and subcombinations ofthe various elements, features, functions and/or properties disclosedherein. No single feature, function, element or property of thedisclosed embodiments is essential. The following claims define certaincombinations and subcombinations which are regarded as novel andnon-obvious. Other combinations and subcombinations of features,functions, elements and/or properties may be claimed through amendmentof the present claims or presentation of new claims in this or a relatedapplication. Such claims, whether they are broader, narrower or equal inscope to the original claims, are also regarded as included within thesubject matter of applicant's invention.

I claim:
 1. A method of repairing a fractured humeral bone in a patient's forearm, comprising: providing a shoulder prosthesis having a shaft; positioning the shaft within the medullary canal of the humeral bone; providing a positioning jig for positioning the shoulder prosthesis at a desired height in the medullary canal; supporting the positioning jig on an exposed region of the humeral bone; and attaching the positioning jig to the shoulder prosthesis to hold the shoulder prosthesis at a desired height relative to the exposed region of the humeral bone.
 2. The method of claim 1 further comprising the step of adjusting the positioning jig to change the height of the shoulder prosthesis relative to the exposed region of the humeral bone.
 3. The method of claim 1, wherein the shoulder prosthesis includes one or more vertically spaced reference marks, and further comprising the step of determining the height of the shoulder prosthesis relative to the humeral bone by noting the position of at least one of the reference marks.
 4. The method of claim 3 further comprising the steps of providing a trial prosthesis having one or more vertically spaced reference marks corresponding to the reference marks on the shoulder prosthesis, and installing the trial prosthesis in the humeral bone and noting the position of a selected one of the reference marks on the trial prosthesis when the trial prosthesis is at the desired height.
 5. The method of claim 4 further comprising the step of positioning the shoulder prosthesis so that the corresponding reference mark on the shoulder prosthesis is in the identical position as the selected reference mark on the trial prosthesis when at the desired height.
 6. The method of claim 1, wherein the positioning jig includes an alignment rod extending transverse to the humeral bone, and further comprising the step of aligning the alignment rod relative to the patient's forearm to position the shoulder prosthesis with a desired retroversion angle in the humeral bone.
 7. A method of repairing a fractured humeral bone in a patient's arm, comprising: providing a shoulder prosthesis having a shaft; positioning the shaft within the medullary canal of the humeral bone; providing a positioning jig for positioning the shoulder prosthesis with a desired retroversion angle in the medullary canal, wherein the positioning jig includes an alignment rod extending from the positioning jig at a predetermined retroversion angle; engaging the shoulder prosthesis with the positioning jig; and aligning the alignment rod relative to the patient's forearm to position the shoulder prosthesis with the predetermined retroversion angle in the humeral bone.
 8. The method of claim 7, wherein the predetermined retroversion angle is 30-degrees.
 9. The method of claim 7 further comprising the step of adjusting the alignment rod to change the retroversion angle.
 10. The method of claim 7, further comprising the step of flexing the patient's arm to approximately 90-degrees between the forearm and humeral bone prior to the step of aligning.
 11. The method of claim 7, wherein the shoulder prosthesis includes one or more angular reference marks, and further comprising the step of determining the retroversion angle of the shoulder prosthesis relative to the humeral bone by noting the position of at least one of the reference marks.
 12. The method of claim 11 further comprising the steps of providing a trial prosthesis having one or more angular reference marks corresponding to the reference marks on the shoulder prosthesis, and installing the trial prosthesis in the humeral bone and noting the position of a selected one of the reference marks on the trial prosthesis when the trial prosthesis is positioned with a desired retroversion angle.
 13. The method of claim 12 further comprising the step of positioning the shoulder prosthesis so that the corresponding reference mark on the shoulder prosthesis is in the identical position as the selected reference mark on the trial prosthesis when positioned with the desired retroversion angle.
 14. A method of placing a shoulder prosthesis in a humeral bone, comprising: providing a positioning jig configured to attach to the shoulder prosthesis; inserting the shoulder prosthesis into the humeral bone; and stabilizing the height of the shoulder prosthesis in the humeral bone by attaching the positioning jig to the shoulder prosthesis and placing at least a portion of the positioning jig against a proximal portion of the humeral bone.
 15. The method of claim 14 further comprising adjusting the height of the shoulder prosthesis by adjusting the distance between the proximal portion of the humeral bone against which the positioning jig is placed and a proximal end of the shoulder prosthesis.
 16. The method of claim 14 further comprising adjusting retroversion by utilizing an elongate sighting arm connected to the positioning jig, where retroversion is adjusted by visually orienting the forearm relative to the sighting arm.
 17. The method of claim 14 further comprising evaluating deltoid tension with the shoulder prosthesis stabilized by the positioning jig.
 18. The method of claim 14 further comprising test fitting one or more trial prosthesis to select the size of the shoulder prosthesis.
 19. The method of claim 14, wherein the shoulder prosthesis is provided with a mount to facilitate rigid attachment of the positioning jig to the shoulder prosthesis.
 20. The method of claim 19, wherein the mount prevents the shoulder prosthesis from rotating relative to the positioning jig.
 21. The method of claim 19, wherein the shoulder prosthesis includes a head positioned to one side of an elongate stem and the mount is located on the head side of the stem.
 22. The method of claim 14, wherein the shoulder prosthesis includes a plurality of vertical height markings, and where the height of the shoulder prosthesis in the humeral bone is established at least partially by reference to the height markings.
 23. The method of claim 14 further comprising securing the shoulder prosthesis in the humeral bone, where the step of securing includes placing a screw through the shoulder prosthesis and the humeral bone.
 24. The method of claim 23, wherein the positioning jig includes a targeting guide configured to facilitate placement of the screw.
 25. The method of claim 14 further comprising testing the height of the shoulder prosthesis by attaching at least one of the tuberosities to the shoulder prosthesis prior to securing the shoulder prosthesis in the humeral bone.
 26. The method of claim 14 further comprising determining a desired position of the shoulder prosthesis in the humeral bone by installing a trial prosthesis and establishing a desired position by adjusting the trial prosthesis.
 27. The method of claim 26, wherein the trial prosthesis and shoulder prosthesis each include vertically spaced markings, and further comprising the step of noting the location of a selected marking on the trial prosthesis relative to a proximal portion of the humeral bone when the trial prosthesis is in the desired position and positioning the shoulder prosthesis in the humeral bone to replicate the location of the selected marking with a corresponding marking on the shoulder prosthesis.
 28. A method of positioning a shoulder prosthesis in a humeral bone, comprising: providing a jig configured to be selectively attached to the shoulder prosthesis, where the jig includes an elongate sighting arm extending generally transverse to the humeral bone; attaching the jig to the shoulder prosthesis; and adjusting the retroversion of the shoulder prosthesis in the humeral bone by visually orienting the elongate sighting arm relative to the forearm.
 29. The method of claim 28, wherein the sighting arm is positioned generally proximal to the forearm.
 30. The method of claim 29, wherein the position of the sighting arm along the humeral bone is adjustable.
 31. The method of claim 28, wherein the sighting arm is oriented parallel to the forearm in the step of adjusting.
 32. The method of claim 31, wherein the angle of the sighting arm with respect to a head axis of the shoulder prosthesis is adjustable.
 33. The method of claim 28 further comprising stabilizing the height of the shoulder prosthesis in the humeral bone by locating a portion of the jig against an exposed portion of the humeral bone.
 34. The method of claim 28 further comprising installing a screw to secure the shoulder prosthesis to the humeral bone, where the jig includes a targeting guide to facilitate installation of the screw.
 35. The method of claim 28 further comprising determining a desired position of the shoulder prosthesis in the humeral bone by installing a trial prosthesis and establishing a desired position by adjusting the trial prosthesis.
 36. The method of claim 35, wherein the trial prosthesis and shoulder prosthesis each include vertically spaced markings, and further comprising the step of noting the location of a selected marking on the trial prosthesis relative to a proximal portion of the humeral bone when the trial prosthesis is in the desired position and positioning the shoulder prosthesis in the humeral bone to replicate the location of the selected marking with a corresponding marking on the shoulder prosthesis. 